What Is An O Specific Polysaccharide? Essay

821 words - 4 pages

The O-specific polysaccharide is a heteropolysaccharide made up of a chain of repeating oligosaccharide units, ( 3 to 8 monosaccharides each) which are strain specific and determinative for the serological identity of the respective bacterium.O-polysaccharides are located on the outer surface exposed to the outer environment of the bacterium. 1-8 glycosyl residues can be seen in O- polysaccharide region as repeating units among various gram negative strains. These sugars varies in their types, sequence, substitution, chemical linkage, ring forms, substitution, presence or absence of non carbohydrate moiety etc giving a heterogenic nature for O-polysaccharides from different gram negative stains (Erridge et al., 2002).The diverse and specific arrangements utilizing various sugar monomers in the O-polysaccharide of LPS generates hundreds of distinct patterns or serotypes for each gram negative bacterial strains in nature. There are approximately 1-50 subunits (repeating units) well represented to complete the O-polysaccharide chain (Erridge et al., 2002). Each subunit encompasses three to eight sugar units and there may be up to fifty identical subunits in an O –chain. Some bacteria display shorter O-chains on average than others. The smooth type Salmonella species are in this category. In some cases, the last sugar unit at the non reducing end of O-chain carries a substituent which blocks the further addition subunits acting as a terminal signal. The sugar monomers in the repeating subunits of O-polysacchride chain may be linear or branched, homopolymers (with a single monosaccharide component) or heteropolymers in which frequently it was seen. A particular gram negative strain can produce multiple O-polysaccharide chain lengths if an incomplete biosynthesis of O-specific chains resulted. This will give LPS a classical ladder pattern of varying molecular weights if silver stained using SDS-PAGE. The O-polysaccharides also known as O-antigens are the major components responsible for the remarkable structural diversity seen in gram negative bacteria (Knirel and Kochetkov., 1994). Since the O-polysaccharide represents the surface antigen (O- antigen), in pathogens these O- chains are in direct contact with the host during infection (Caroff and Karibian 2003). Their antigenic nature forms the basis for serotype classification among various bacterial families (Wilkinson, 1996; Holst et al., 1998). O- antigens are present only in smooth type of gram negative bacteria. The repeating subunits of o-antigen appears extending out from the surface of gram negative outer wall. More than sixty monosaccharide units have been recognized...

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